THE VULNERABILITY OF BARRIER ISLANDS TO CHANGE DURING EXTREME STORMS

The vulnerability of barrier islands to change during extreme storms can be assessed using a ‘storm impact scale' that incorporates both forcing processes and coastal morphology. The maximum amount of island change is likely to occur during inundation regime, when the elevation of storm surge exceeds the elevation of dune crests. Under this condition, the island is continuously underwater, rather than experiencing the periodic submergence that occurs during overwash. Inundation can occur locally, resulting in a breach that severs a barrier island, or along the entire island length, resulting in catastrophic land loss, like the 85% loss in surface area of the Chandeleur Islands, Louisiana during Hurricane Katrina. Assessments of potential inundation regime locations have been made for the barrier island coasts of the southeast U.S. for Category 1 – 5 hurricanes. Maximum storm surge for each category was estimated using the National Hurricane Center's SLOSH model runs, where hurricanes of different intensities, directions and forward speeds are simulated to determine the worse case storm surge. Surge estimates along the open coast are compared to dune elevations at the same locations. Dunes are surveyed by airborne lidar, as part of a cooperative coastal mapping effort between USGS, NASA, and the Corps of Engineers. The differences between surge estimates and dune elevations show the magnitudes and spatial variations of barrier-island vulnerability to coastal change during extreme storms.